More and more studies are reporting climate change as the main culprit for not only species adaptation, but also for changes in population size. But a new study shows that population increases or decreases cannot only be attributed to increasingly warmer weather and that multiple factors play a role when it comes to species population.

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A 32-year study of subarctic forest moths provides insight on how roles of ecological forces can affect populations, proving increased precipitation and warmer temperatures affects the rate of population growth.

"Every time the weather was particularly warm or particularly wet, it had a negative impact on the rates at which the populations grew," said Mark Hunter, the Henry A. Gleason Collegiate Professor in the University of Michigan Department of Ecology and Evolutionary Biology.

"Yet, overall, most of these moth populations are either stable or increasing, so the only possibility is that something else other than climate change—some other factor that we did not measure—is buffering the moths from substantial population reductions and masking the negative effects of climate change."

If unknown ecological forces are helping to counteract the harmful effects of climate change on these moths, it's conceivable that a similar masking of impacts is happening elsewhere. If that's the case, then scientists are likely underestimating the harmful effects of climate change on animals and plants, Hunter said.

Hunter and six Finnish colleagues report their findings in a paper published in the journal Global Change Biology.

Between 1978 and 2009, Finnish scientists used light traps at night to catch 388,779 moths from 456 species at the Värriö Strict Nature Reserve, 155 miles north of the Arctic Circle.

Hunter used a statistical technique to examine how various ecological forces, including climate, affected per capita population growth.

Most recent studies of moth abundance have shown population declines. So Hunter and his colleagues were surprised to find that 90 percent of the moth species in the Lapland study were either stable or increasing.

On one level, the results can be viewed as a good news climate story: In the face of a rapid environmental change, these moths appear to be thriving, suggesting that they are more resilient than scientists had expected, Hunter said.

However, the study also reveals that unknown ecological forces appear to be buffering the harmful effects of climate change and hiding those impacts from view. The results demonstrate that "simple temporal changes in population abundance cannot always be used to estimate effects of climate change on the dynamics of organisms," the authors conclude.